Medical treatment of many illnesses requires continuous (or periodic) drug infusion into various parts of the body via subcutaneous and/or intravenous injections. Diabetes mellitus patients, for example, require the administration of varying amounts of insulin throughout the day to control their blood glucose levels. In recent years, ambulatory portable insulin infusion pumps, employing continuous subcutaneous insulin infusion (CSII), have emerged as a superior alternative to multiple daily injections (MDI) of insulin for Type 1 and Type 2 diabetes patients using syringes. These pumps, which deliver insulin at a continuous basal rate, as well as in bolus volumes, were developed to liberate patients from repeated self-administered injections, and allow them to maintain a near-normal daily routine. Both basal and bolus volumes must be delivered in precise doses, according to individual prescription, because an overdose or underdose of insulin could be fatal.
Insulin Pumps Evolution
The first generation of portable insulin pumps includes a “pager like” device with a driving mechanism including motor and gears, and a reservoir contained within a housing. Examples of such devices are described, for example, in U.S. Pat. Nos. 6,248,093 and 7,390,314. In conventional configurations, a driving mechanism, which includes a motor, a gear and a drive screw, moves a plunger inside a syringe (reservoir) to deliver insulin into the user's body. For example, as the motor rotates a gear, a threaded drive screw is rotated. The plunger of the syringe has an elongated member shaped like a cylinder which is internally threaded for engagement with the drive screw. As a result, the motor rotates the drive screw which engages the threads of the cylinder and converts the rotation of the drive screw into a linear motion to displace the plunger in an axial direction. These first generation devices represent a significant improvement over multiple daily injections (MDI), but are typically large sized, heavy weighted, and have long tubing.
To ease the use of portable insulin pumps, second generation pumps were proposed. Second generation pumps are based on use of a remote-controlled skin adherable device having a bottom surface adapted to be in contact with a patient's skin. A reservoir is contained within the housing and can be filled using an additional syringe. The additional syringe is used to draw medicine from a vial and then inject the medicine into the reservoir. This concept is discussed, for example, in U.S. Pat. Nos. 5,957,895, 6,589,229, 6,740,059, 6,723,072, and 6,485,461. These second generation devices generally have to be disposed of every 2-3 days (e.g., due to insertion site infections and reduced insulin absorption), including all the expensive components, such as electronics and the driving mechanism.
A third generation pump was developed to avoid the cost issues associated with the second generation devices and to expand patient customization. An example of a third generation device is disclosed, for example, in co-owned, co-pending U.S. Patent Application Publication No. 2007-0106218, and in co-owned International Patent Application Publication No. WO/2007/052277, the contents of all of which are hereby incorporated by reference in their entireties. Such a third generation device contains a remote control unit and a skin-adherable patch unit that may include two parts: (1) a reusable part containing the electronics, at least a portion of the driving mechanism and other relatively expensive components, and (2) a disposable part containing the reservoir and, in some embodiments, at least one power source (e.g., a battery).
A further improvement to the skin adherable pump that includes two parts is described, for example, in co-owned, co-pending U.S. Patent Application Publication No. 2008-0215035 and in co-owned International Patent Application Publication No. WO/2008/078318, the contents of all of which are hereby incorporated by reference in their entireties. The disclosed device is configured as a dispensing unit that can be disconnected from and reconnected to a skin-adherable cradle unit. Such skin-securable dispensing units can be remotely controlled and/or operated by a user interface (e.g., a buttons-based interface) provided on a housing of the dispensing unit, as disclosed, for example, in co-owned International Patent Applications Publication Nos. WO/2009/013736 and WO/2009/016636, the contents of all of which are hereby incorporated by reference in their entireties.
An insulin infusion device may be integrated with a continuous glucose monitor (CGM) enabling open and/or closed loop systems. Such a device integrating insulin delivery and glucose monitoring is disclosed, for example, in co-owned, co-pending U.S. Patent Applications Publication Nos. 2007-0191702 and 2008-0214916, and in co-owned International Patent Applications Publication Nos. WO/2007/093981 and WO/2008/078319, the disclosures of which are incorporated herein by reference in their entireties.
Occlusion and Malfunctions Detection
An occlusion occurs when an infusion line (e.g., a tube, a cannula) is blocked. This is typically expressed as a kink in the infusion line, but in infusion lines delivering insulin, an occlusion may further occur because of insulin crystallization. Accordingly, an occlusion may cause under-infusion of insulin to the user's body, which may have significant health effects such as hyperglycemia. Most insulin pager pumps have an occlusion detection mechanism based on direct or indirect measurement of pressure elevation. When the therapeutic fluid (e.g., insulin) is to be delivered from a reservoir of the device into the user's body via a needle/cannula and an occlusion occurs, pressure is built up in the reservoir. Direct pressure measurement is the monitoring of force over the driving mechanism (pressure defined as force per unit area), while indirect pressure measurement relates to the monitoring of the motor's power (e.g., torque) or rotation of the motor shaft (also referred to as “motor rotation” or “rotation of the motor”). Pressure elevation hinders the rotation of the motor and/or gear (hereinafter “driving mechanism”), and may occasionally even cause cessation of motor operation. In other words, power provided to the motor will not result in rotation of the motor.
Occlusion detection by indirect pressure measurement is described, for example, in U.S. Pat. Nos. 6,362,591, 6,555,986 and 7,193,521. In these examples, electrical current to an infusion pump's motor is measured and compared against a baseline average current, which must first be established when there is no occlusion condition. If the current exceeds a threshold, an occlusion alarm is triggered. According to these patents, measurement of current can also provide feedback to the controller of driving mechanism performance, with the aid of a driving mechanism rotation monitor (also referred to as an “encoder”), e.g., in case of a failure of the gearbox, the motor cannot rotate, the measured current is high and the encoder indicates that the driving mechanism is faulty. However, these references do not describe how to distinguish between an occlusion and a driving mechanism malfunction. Moreover, generally, when there is only one monitoring element (e.g., an encoder, current measurement), the controller cannot distinguish between an occlusion and a driving mechanism malfunction.
Other circumstances may also provide “occlusion-like” indications when only one monitoring mechanism is applied. Therefore, in order to distinguish occlusion related errors from other errors, at least two parameters related to the therapeutic fluid delivery generally have to be monitored. Typically, an encoder is used to monitor the driving mechanism and a separate monitoring mechanism is used for occlusion detection.
Such an occlusion monitoring/detection mechanism may include a pressure gauge, a flow meter, or a load cell, all of which take up space, and require additional power supply and dedicated signal/data processing. An example of such an occlusion monitoring/detection mechanism based on force measurements is described, for example, in U.S. Pat. No. 5,647,853.
The occlusion monitoring/detection mechanism may also malfunction and usually another monitoring instrument/device is required. For example, in U.S. Pat. No. 7,193,521, readings of a force sensor are compared to a position of the plunger to verify its proper condition.